Digital Electronics: Principles, Devices and Applications

568 Digital ElectronicsFromSensorsTo ActuatorsKeyboard,Displaysetc.A/DConverterD/AConverterParallelPortsSerialPortsCounters/TimersCentralProcessingUnitMemorySFRsFigure 14.3Inside the microcontroller.Timer InputSystemClockFree-RunningCounterTimer OutputSystemFigure 14.4Timer subsystem.14.2.1 Central Processing Unit (CPU)The central processing unit processes the program. It executes the instructions stored in the programmemory pointed to by the program counter in synchronization with the clock signal. The processorcomplexity could vary from simple eight-bit processors to sophisticated 32-bit or even 64-bit processors.Some common microcontrollers using eight-bit processors include 68HC11 (Freescale Semiconductor– earlier part of Motorola), the 80C51 family of microcontrollers (Intel and Dallas Semiconductor),Zilog-eZ8 and Zilog-eZ80 (Zilog) and XC800 (Infineon). Examples of microcontrollers using 16-bitprocessors include the 8096 family (Intel), 68HC12 and 68HC16 (Freescale Semiconductor), theF2MC family (Fujitsu) and the XC166 family (Infineon). Examples of microcontrollers using 32-bit processors include 683XX, MPC 860 (PowerQUICC), MPC 8240/8250 (PowerQUICC-II) andMPC 8540/8555/8560 (PowerQUICC-III) (all from Freescale Semiconductor), the TRICORE family(Infineon) and the FR/FR-V family (Fujitsu).